RE: CCL:A question on DFT

[David Heisterberg <dheister %-% at %-% chemistry.ohio-state.edu>]

>> Yes, any density can be represented as a single slater determinant
 >If the density should correspond to a pure
 >spin state (pure <s**2>) it can in general NOT
 >be represented by a single determinant and this
 The proof that any reasonable density may be obtained from
 a single determinant of orthonormal orbitals is pretty
 straight-forward, and is by construction.  The resulting
 iso-density orbitals may not look anything like typical HF
 or DFT orbitals, however.  I'm sure Mel Levy discusses this
 in a few papers.
 It is not the case that every reasonable first order density
 matrix may be obtained from a single determinant.
 What constitutes reasonable is integrability (or some sort
 of normalizability in the case of continuum states) and
 sufficient smoothness which more or less implies finite
 kinetic energy.
 Dave Heisterberg